Acoustic delay lines



Nov. 17, 1959 v. J. PORTER ETAL 2,913,680

ACOUSTIC DELAY LINES Filed Aug. 18, 1955 Bus Source SignclOul' INVENTORS VINCENT J. PORTER BY MARK NA/MAN AGENT United States Patent AcoUsTIo DELAY LINES Vincent J. Porter, Huntingdon Valley, and Mark Naiman,

Philadelphia, Pa., assignorsto Sperry Rand Corporation, New York, N.'Y., a corporation of Delaware The present invention-relates to acoustic delay lines and is more particularly concerned with novel delay line structures exhibiting a larger delay per unit length than may be obtained from acoustic delay lines known heretofore; l i

--Acoustic delay lines are presently utilized in many electronic applications, and may be employed for instance in' memories for use in computing apparatuses. Reference is made to US. Patent No. 2,629,827 to J. P. Eckert, Jr., issued February 24, 1953, for Memory Systern, which patent discusses various forms of acoustic delay line structures which may be employed in computer memories. In general, such a memory operates in conjunction with recirculation means such as an amplifier, whereby information to be stored as a pulse sequence may'be fed to one end of the acoustic delay line,-may be caused to propagate as an acoustic signal downfthe said delay line, and may then be caused to recirculat'e to-the input of the line. Inasmuch as the acoustic propagation down such a'line takes a finite time, the successive recirculation? of information through an acoustic delay line, of the type contemplated, effectively stores the information being recirculated.

The foregoing Eckert patent discloses various forms of delay lines capable of functioning in the above described manner, and'such delay lines may take the form of an elongated rod, tape, wire, or tube, for instance, of and acoustic transmission medium. acoustic transmission medium described in the said Eckert patent employs, for instance, magnetostrictive materials. In general, while the particular configurations of solid acoustic delay lines discussed in Eckert Patent 2,629,827, identified above, provide good results in memory systems, it has been found that the acoustic transmission mediums, when taking the configuration of an elongated substantially straight body of acoustic transmission material, exhibit an extremely high velocity of sound propagation. As a result, when such lines are to be utilized at relatively low frequencies of operation, for instance at pulse rates of a hundred. or so kilocycles, the storage of information in the .line is relatively inefficient, and information pulses may be spread out along the line at any given instant so as to occur, perphaps, inches apart.

The present invention serves to obviate the foregoing .difiiculty and provides acoustic delay lines which are capable of storing pulses more eificiently and at higher density when lower pulse repetition rates are employed, then has been the case heretofore. In addition, due to the concepts of the present invention, the improved delay lines to be described are adapted to provide acoustic matching of the impedance of acoustic transducers more readily than has been the case heretofore.

"It is accordinglyfan object of the present invention to provide improved acoustic delay lines. a

V A further object of the present invention resides inthe provision of acoustic delay lines which may be 2,913,680 Patented Nov. 1 7, 1959 '2 smaller in physical configuration than has been the case heretofore.

A still further object of the present invention resides in the provision of an elongated acoustic delay line exhibiting a greater delay per unit length than has been the case heretofore whereby shorter lines may be utilized to provide a desired delay than has been the case in the past.

A further object of the present invention resides in the provision of an acoustic delay line providing greater efficiency of operation at relatively low pulse repetition rates.

A further object of the present invention resides in the provision of an improved acoustic delay line capable of being more readily and accurately acoustically matched to the impedance of acoustic transducers than has been the case heretofore.

The foregoing objects and advantages of the present invention are efiected, as will be described, by the provision of delay lines exhibiting a constantly varying acoustic impedance between spaced points on the line;

' In accordance with preferred embodiments of the present constant acoustic impedance, and as a result, more pulses One particular 7 may be stored per unit length inthe line.

The foregoing construction and operation of the present invention will become, more readily apparent from the following description and accompanying drawings, in which: V s

Figure 1 illustrates an improved acoustic delay line constructed in accordance with one embodiment of the present invention, 7

FigureZ illustratesa modified form of acoustic delay line constructed in accordance with a further embodi ment of the present invention; and

Figure 3 illustrates astil-l further embodiment of the present invention wherein variations in acoustic impedance may be introduced magnetically.

Referring now to Figure 1, it Will be seen that, in accordance with the present invention, an acoustic delay line may'ta-ke the form of an elongated bar, tube, tape, or wire 10, constructed of a suitable acoustic transmiss'ion medium. Acoustic transducer 11 may be disposed adjacent one end of the said transmission medium '10 for the selective propagation of acoustic waves down the medium 10; and a further acoustic transducer 12 may be disposed adjacent the other end of the said medium 10 for the detection or interception of acoustic waves propagated in medium 10 by transducer 11.

- As has been mentioned previously, the medium 10 may comprise magnetostrictive material for instance, in which eventjthe acoustic transducers 11 and 12 may comprise, as shown, magnetic transducers. When this particular embodiment of the present invention is employed, the

transducers 11 and 12 may each include a pair of wind ings, as shown; and these windings may in'turn take the form of signal windings 13 and 14 and bias windings 15 and 16. :In addition, if'the structure of Figure 1 is to be employed in a recirculating memory, for instance, a recirculating amplifier may be disposed between signal 0 output winding 14 on transducer 12 and signal input winding 13 on transducer 11 thereby to provide a'continual recirculation of information through the acoustic 7 transmission medium 10.- Thefore'going form of acoustic delay line is essentially shown in the aforementioned patent to Eckert No. 2,629,827, and in particular, in Figures 23 through 25 thereof.

If the acoustic transmission medium should take the form of a substantially straight rod, tube, wire or the like, as described in the said Eckert patent, whereby the medium exhibits a substantially constant acoustic impedance between the acoustic transducers Hand 12, the operation of the device at relatively low acoustic pulse rates becomes inefficient. In accordance with one embodirnent of the present invention, the efiiciency of acoustic delay lines such as have been described, may be enhanced considerably by causing the said line to exhibita plurality of variations in acoustic impedance between acoustic transducers adjacent the said line.

In the particular embodiment of Figure 1 these variations in acoustic impedance may be efiected by causing the transmission medium 10 to exhibit a plurality of changes in cross-dimension. Thus, referring to Figure 1, it will be seen that the surface of transmission medium 10 may assume a configuration exhibiting knobs or lumps 17 whereby the cross-dimension of the medium 10 is causedto change regularly between values arbitrarily termed A and B, in Figure 1. The medium 10 may take the form of a flat rod or wire whereby the knobs 17 may be formed as a series of corrugations on the upper and lower surfaces thereof. In the alternative, the several knobs 17 may exhibit circular symmetry with respect to the elongated axis of medium 10 whereby the changes in cross-dimension take the form of a plurality of bulbs adjacent one another along. the length of medium 10.

In accordance with preferred forms of the presentinvention, the variationsin acoustic impedance defined by the configuration shown in Figure 1, may occur cyclically and this cyclic variation should occur at a rate which is relatively high in comparison to the repetition rate of acoustic waves being propagated down the line, i.e. there should be a plurality of variations in acoustic impedance in each space between successive pulses being propagated down the delay line. The particular curvature defined by the peripheral surfaces of the several knobs 17 may conformto any desired law, but in accordance with a preferred embodiment of the present invention, the curvature may follow, in both expansion and contraction, an exponential law. When this latter form of the invention is practiced, an analogy may be drawn between the resultant acoustic delay line and exponential horns acting as acoustical transformers, for it is known in the art that by providing an exponentially expanding acoustical wave guide, transformations in impedance may be eifected substantially without reflection.

Whatever the particular law utilized in defining the increasing and decreasing cross-dimension of the transmission medium 10 however, it will be appreciated that by the plurality of variations in acoustic impedance the delay line tends to assume a lumped characteristic whereby pulses are propagated down the line at a lower velocity than would be the case with an unlumped line; and accordingly, a higher density of pulse storage may be effected, with a resultant increase in efiiciency of operation. The particular transmission medium 10 shown in Figure 1 may assume a tubular configuration, in which event the portions 17 may take the form of an increasing and decreasing thickness of tube wall. When tubular delay lines are to be employed, however, the invention may be practiced more readily in accordance with the embodiment illustrated in Figure 2. Thus, referring to Figure 2, it will be seen that an improved acoustic delay line exhibiting the lumped characteristic described above, may be provided by a tubular transmission medium 20 associated with a pair of acoustic transducers 21 and 22. The variation in,cros s-dimension and resultant variation in acoustic impedance, may be effected in this latter embodimerit of the present invention by forming an elongated slot in a wall of tube 20 and this slot may in turn take agated.

While the particular embodiment of Figure 2 has illustrated the provision of a single variable width slot disposed substantially parallel to the elongated central axisrof tubular'transmission medium 20, it will be appreciated that the effective variation in cross-dimension may be accomplished by the provision of a plurality of such slots or by a plurality of difier'ently dimensioned slots giving the desired changes in efiective cross-dimension at adjacent points along the line. In addition, the slot or slots defined in the wall of tube 20 may be substantially straight, as described, or they may be helically disposed;

about the periphery of the tube 20 as may be desired.

Each of the embodiments, described ,in jreference .to Figures 1 and 2 has eifected the desired variation in acoustic impedance by a change in the physical dimensions of the acoustic transmission medium between spaced .acous tic transducers. This desired variation in acousticimpedance may be effected in other ways, one such method is illustrated in Figure 3 wherein the variation is accomplished magnetically. Reference is made to the copending application of. Theodore H. Bonn, Serial No, 499,285, filed April 5,, 1.955, for: Variable DelayLine now US. Patent No. 2,814,-

793, issued November 26, 1957. This patent is assigned ic transducers and by applying suitablebias, potentials tov the said elongated coil thereby to cause the magnetostrictive material to operate over a selected portion of its hysteresis curve. 7 a

As has been discussed intbe above identified patent,

the velocity of acoustic transmission in a magnetostrictive material is represented by the equationzw between spaced acoustic transducers, and the bias potential is caused to be constant or to vary relatively slowly in comparison with the repetition rate of acoustic waves, thereby to effect the desired control in time delay.

For any given acoustic wave being propagated, however, the acoustic impedance of the line is substantially constant between acoustic transducers. of delay line, however, may be readily modified in accordance with the concepts of the present invention to provide a more efificient delay line.

Thus, referring to Figure 3, it will be seen that, in; accordance with this further form of the present inven-' t1on, an acoustic delay linemay comprise an elongated transmission medium 36' associated with acoustic trans-.

ducers 31 and 32 This'medium 30 may, as described,

take the form of a magnetostrictive red, tube, wire or tape, in which event the transducers 31' and 32 may S IT PH magnetic transducers. An elongated bias coil #3 1S sed about th t ansm ss an edium 5 between This particular form the transducers 31 and 32, and the said coil 33 is coupled to terminals 34, to which terminals may be applied a suitable source of bias potential. If the winding 33 exhibits a substantially uniform pitch between transducers 31 and 32, the concepts of the present invention may be practiced by causing the bias source 34 to vary at a rate which is relatively high in comparison with the repetition rate of acoustic waves being propagated through the medium 30, whereby the said medium 30 exhibits an acoustic impedance which cyclically changes at a time rate which is substantially higher than the frequency of acoustic waves.

The particular form of the invention shown in Figure 3 may also effect the desired variation in acousticimpedance by causing the winding pitch of coil 33 to vary between the transducers 31 and 32. Figure 3 has been particularly directed to this form of the invention wherein a constant variation in winding pitch is employed. When this varying winding pitch is provided, the bias source applied to terminals 34 may assume a relatively constant value or may vary at a rate relatively low in comparison to the repetition rate of acoustic waves. It will be appreciated, however, that the flux induced at any portion of the magnetostrictive material 30 by the elongated winding 33 is related to the number of turns per inch of the coil 33, in the area of the portions. A soft iron outer sleeve 35 may be placed over the medium 30 and coil 33 to provide local magnetic return paths.

Thus, due to the constant or cyclic variation in winding pitch of coil 33, the effective magnetic bias provided by source 34 cyclically varies from portion to portion along the transmission medium 30, and this cyclic variation in bias eifects a cyclic variation in the velocity of acoustic propagation (in accordance with the formula given above), whereby there is a resultant cyclic variation in acoustic impedance along the line. Again, therefore, the resultant acoustic delay line exhibits a lumped characteristic whereby the effective velocity of wave propagation in the line is slower, and the efiiciency of the line at low pulse rates is higher, than has been the case heretofore.

While preferred embodiments of the present invention have been described, many variations will be suggested to those skilled in the art. The foregoing description is therefore meant to be illustrative only and should not be considered limitative of our invention, and all such variations as are in accord with the principles described are meant to fall within the scope of the appended claims.

Having thus described our invention, we claim:

1. An acoustic delay line comprising an elongated acoustic transmission medium of tubular configuration, first and second acoustic transducers spaced from one another along said medium for selectively impressing and detecting a plurality of acoustic pulses in said medium, said pulses being spaced from one another along said medium and being propagated along said medium in said spaced relation between said transducers, said tubular medium including elongated aperture means cyclically varying in cross-dimension whereby said medium defines a smoothly increasing and decreasing cyclically varying acoustic impedance between said first and second transducers, the spacing between said acoustic pulses being such that there are a plurality of said increases and decreases in acoustic impedance in said medium in each of the spaces etween successive ones of said acoustic pulses.

2. The delay line of claim 1 wherein said transmission medium comprises magnetostrictive material, said 5 acoustic transducers comprising magnetic transducers movably mounted adjacent said medium.

3. In combination, an acoustic delay line comprising an elongated magnetostrictive acoustic transmission medium, said transmission medium including an elongated 10 tube of magnetostrictive material having a substantially constant diameter, a first magnetic transducer adjacent one end of said magnetostrictive medium for producing a plurality of acoustic waves in said medium, said acoustic waves being spaced from one another along said medium and being propagated in said spaced relation from said one end of said medium toward the other end of said medium, a second magnetic transducer adjacent the other end of said medium for detecting successive ones of said spaced acoustic Waves, said medium having a plurality of smoothly increasing and decreasing cyclically spaced variations in cross-sectional area along said medium be tween the ends thereof, the spacing between successive ones of said propagated acoustic waves being related to the spacing between said variations in cross-sectional area of said medium whereby said medium defines a plurality of said cyclic variations in cross-sectional area in each space between successive ones of said spaced acoustic waves, said variations in cross-sectional area of said medium being efiected by elongated slot means defined in the walls of said tube, said slot means having cyclic variations in cross dimension along said medium.

4. The combination of claim 3 including means coupling the output of said second transducer to the input of said first transducer whereby said spaced acoustic Waves are recirculated between said transducers via said elongated magnetostrictive transmission medium.

5. An acoustic delay line comprising an elongated acoustic transmission medium for the propagation of spaced acoustic waves therein, said elongated acoustic transmission medium being tubular in configuration, said transmission medium including a plurality of adjacent sections each of which has an acoustic impedance smoothly varying between first and second limits, said transmission medium including a plurality of said smooth variations in acoustic impedance in each space between successive ones of said acoustic Waves in said elongated medium. said variations in acoustic impedance being eifected by an elongated slot of cyclically varying width defined in said tubular medium. 50

References Cited in the file of this patent UNITED STATES PATENTS Adler Mar. 21, 1950 Frederick Aug. 28, 1951 Burns et al. July 29, 1952 Eckert et al Feb. 24, 1953 OTHER REFERENCES 

